Here's a quick and dirty guide to convert a Foscam FI9903P (non-PoE), to be able to be feed the 12Vdc using the pairs that are not used (4-5,7-8).
Steps:
1- Open your camera, removing the 4 hex screws on the front side of the camera, this will void the warranty...
2- Locate the connector that brings the ethernet signals from the external connectors to the boards.
3- Disconnect the cable and take out the pins 3 and 4 (light gray and orange).
4- Solder the light gray cable to the black cable (power -)
5- Solder the orange cable to the red cable (power +)
6- Close the camera
7- Connect your 12Vdc PoE to the ethernet input of the camera, the camera should boot.
8- Smile! (you saved like $50 for a similar camera with PoE...)